Radio communication system, radio station, radio terminal, communication control method, and non-transitory computer readable medium

ABSTRACT

A radio terminal can perform carrier aggregation using a first cell of a first radio station and a second cell of a second radio station. The first radio station performs, with the radio terminal, radio resource control for the first cell and the second cell in order to perform the carrier aggregation. Further, the first radio station transmits, to the second radio station, update information regarding an update to a configuration related to the radio resource control for the second cell. It is thus, for example, possible to prevent or reduce data transmission/reception failures which would otherwise occur while a configuration of radio parameters or the like is being changed by a radio terminal in carrier aggregation of a plurality of cells served by different radio stations.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation application of U.S. patentapplication Ser. No. 16/708,738 filed on Dec. 10, 2019, which is aContinuation application of U.S. patent application Ser. No. 15/844,126filed on Dec. 15, 2017, which is issued as U.S. Pat. No. 10,536,930,which is a Continuation application of U.S. patent application Ser. No.14/766,010 filed on Aug. 5, 2015, which is issued as U.S. Pat. No.9,961,672, which is a National Stage Entry of international applicationPCT/JP2014/000454 filed on Jan. 29, 2014, which claims the benefit ofpriority from Japanese Patent Application 2013-033704 filed on Feb. 22,2013, the disclosures of all of which are incorporated in their entiretyby reference herein.

TECHNICAL FIELD

The present invention relates to a radio communication system in which aradio station communicates with a radio terminal by using a plurality ofcells.

BACKGROUND ART

In order to improve the deterioration of communication quality due todrastic increases in mobile traffic in recent years and achieve fastercommunication, the standardization of Carrier Aggregation (CA) functionsthat enable a radio terminal (User Equipment (UE)) to communicate with aradio base station (eNode B (eNB)) by using a plurality of cells hasbeen undertaken in the 3GPP Long Term Evolution (LTE). Note that thecells that a UE (User Equipment) can use in CA are limited to aplurality of cells of one eNB (i.e., a plurality of cells served by oneeNB).

The cells that are used by a UE in CA are categorized into a PrimaryCell (PCell) that has already been used as a serving cell when the CA isstarted and a Secondary Cell(s) (SCell(s)) that is used in addition tothe PCell or in dependence thereon. Each SCell can be used by a UE asthe need arises, and the use of them can be stopped. Note that startingthe use of an SCell is called “activating” or “activation”. Similarly,stopping the use of an SCell is called “deactivating” or “deactivation”.Non-Access Stratum (NAS) mobility information, security information(security input) and the like are transmitted and received through aPCell during radio connection (re)-establishment (RRC connectionEstablishment/Re-establishment) (see Non-patent Literature 1). Adownlink (DL) Carrier and an uplink (UL) Carrier corresponding to aPCell are called “DL Primary Component Carrier (PCC)” and “UL PCC”,respectively. Similarly, a DL Carrier and a UL Carrier corresponding toa SCell are called “DL Secondary Component Carrier (SCC)” and “UL SCC”,respectively.

An operation that is performed to change a radio resource configuration(i.e., RRC information) in an SCell when downlink data (DL data) istransmitted/received in CA is explained with reference to FIG. 11(Non-patent Literature 2). Here, it is assumed that a UE uses a firstcell (Cell1) and a second cell (Cell2) served by an eNB as a PCell andan SCell, respectively. In a step S1, the eNB transmits, to the UE,configuration information for the SCell (i.e., the Cell2) (RRCConnection Reconfiguration (SCell configuration)). In a step S2, the UEperforms configuration of radio parameters and the like for the SCell(i.e., the Cell2) (SCell configuration). In a step S3, the UE reportsthe completion of the configuration of the SCell to the eNB (RRCConnection Reconfiguration Complete).

In a step S4, the eNB transmits to the UE an instruction about the startof the use (called “Activation”) of the SCell (Activation controlelement (activation of SCell)). In a step S5, the UE starts to use theSCell (SCell activation). In steps S6 and S7, the eNB transmits DL datato the UE by using the PCell or the SCell, or both of them.

In a step S8, the eNB determines that it needs to change the radioresource configuration of the SCell (i.e., the Cell2) and hencetransmits to the UE the configuration information related to the SCellthat should be changed (RRC Connection Reconfiguration (SCellmodification)). In a step S9, the UE updates the configuration of theSCell (SCell modification). In a step S10, the UE reports, to the eNB,the completion of the configuration change of the SCell (RRC ConnectionReconfiguration Complete). Note that the eNB does not transmit DL datato the UE in the SCell (i.e., the Cell2) until the eNB receives thereport of configuration change completion from the UE.

In steps S11 and S12, the eNB transmits DL data to the UE by using thePCell or the SCell, or both of them.

A radio resource configuration of the SCell in the CA can beappropriately changed through the procedure shown in FIG. 11. Note thatdata transmission/reception is suspended while the eNB and the UE isconfiguring or updating radio parameters and the like by the RRCConnection Reconfiguration. For example, the eNB suspends DL datatransmission to the UE and the UE suspends the DL data reception fromthe eNB.

CITATION LIST Non Patent Literature

-   Non-patent Literature 1: 3GPP TS 36.300 V11.3.0, “Evolved Universal    Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial    Radio Access Network (E-UTRAN); Overall description; Stage 2    (Release 11)”, Section 7.5, September 2012-   Non-patent Literature 2: 3GPP TS 36.331 V11.2.0, “Evolved Universal    Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC);    Protocol specification (Release 11)”, Section 5.3.5.3, December 2012-   Non-patent Literature 3: 3GPP RWS-120046, Samsung Electronics,    “Technologies for Rel-12 and Onwards”, 3GPP TSG RAN Workshop on    Rel-12 and Onwards, Ljubljana, Slovenia, 11-12 Jun. 2012-   Non-patent Literature 4: 3GPP RWS-120010, NTT DOCOMO, “Requirements,    Candidate Solutions & Technology Roadmap for LTE Rel-12 Onward”,    3GPP TSG RAN Workshop on Rel-12 and Onwards, Ljubljana, Slovenia,    11-12 Jun. 2012

SUMMARY OF INVENTION Technical Problem

Further, inter-base station carrier aggregation (inter-eNB CA) in whichcells of different radio base stations (eNBs) are simultaneously usedhas been proposed (Non-patent Literatures 3 and 4). For example, a cellof a macro base station (Macro eNB (MeNB)) and a cell of a low-powerbase station (Low Power Node (LPN)) are simultaneously used as a PCelland an SCell, respectively. In inter-base station (or inter-eNB) carrieraggregation, bearers are independently configured in the PCell and theSCell and communication is performed between an UE and the MeNB andbetween the UE and the LPN.

In the inter-eNB CA, it is also conceivable that the MeNB controls theconfiguration of radio parameters and the like of both the PCell and theSCell. However, for example, when the MeNB attempts to change radioparameters or the like of the SCell in a manner similar to that forordinary CA (i.e., intra-eNB CA) when DL data is being transmitted inthe SCell, the UE suspends the reception of the DL data in the SCellwhile the UE is changing radio parameters of the SCell under theinstruction from the MeNB. Meanwhile, it is conceivable that the LPNthat serves the SCell does not recognize that the UE is changing theradio parameter and thus continues to transmit the DL data. Accordingly,the transmission of the DL data that is performed when the UE ischanging the radio parameter fails, thus possibly causing packet lossesat the worst.

One of the objects of the present invention is to provide a radiocommunication system, a radio station, a radio terminal, a communicationcontrol method, and a program which are contribute to prevention orreduction of data transmission/reception failures which would otherwiseoccur while configuration of radio parameters or the like is beingchanged by a radio terminal in carrier aggregation of a plurality ofcells served by different radio stations.

Solution to Problem

In a first aspect, a radio communication system includes a first radiostation that serves a first cell, a second radio station that serves asecond cell, and a radio terminal capable of performing carrieraggregation using the first and second cells. The first radio station isconfigured to perform, with the radio terminal, radio resource controlfor the first and second cells in order to perform the carrieraggregation. The first radio station is also configured to transmit, tothe second radio station, update information regarding an update to aconfiguration related to the radio resource control for the second cell.

In a second aspect, a first radio station that serves a first cellincludes a communication control unit. The communication control unitsupports carrier aggregation using the first cell and a second cellserved by a second radio station. The communication control unitperforms, with a radio terminal, radio resource control for the firstand second cells in order to perform the carrier aggregation. Further,the communication control unit transmits, to the second radio station,update information regarding an update to a configuration related to theradio resource control for the second cell.

In a third aspect, a second radio station that serves a second cellincludes a communication control unit. The communication control unitsupports carrier aggregation using a first cell served by a first radiostation and the second cell. The communication control unit receives,from the first radio station, update information regarding an update toa configuration related to a radio resource control for the second cell.The radio resource control is performed between the first radio stationand a radio terminal.

In a fourth aspect, a radio terminal includes a communication controlunit that supports carrier aggregation using a first cell served by afirst radio station and using a second cell served by a second radiostation. The communication control unit performs, with the first radiostation, radio resource control for the first and second cells in orderto perform the carrier aggregation. Further, the communication controlunit receives, from the first radio station, configuration informationrelated to the radio resource control for the second cell.

In a fifth aspect, a communication control method in a first radiostation that serves a first cell includes:

(a) performing, with a radio terminal, radio resource control for thefirst cell and a second cell served by a second radio station, in orderto perform a carrier aggregation using the first and second cells; and(b) transmitting, to the second radio station, update informationregarding an update to a configuration related to the radio resourcecontrol for the second cell.

In a sixth aspect, a communication control method in a second radiostation that serves a second cell includes receiving, from a first radiostation, update information regarding an update to a configurationrelated to radio resource control for the second cell. The radioresource control is performed between the first radio station and aradio terminal for carrier aggregation using a first cell served by thefirst radio station and the second cell.

In a seventh aspect, a communication control method in a radio terminalincludes performing, with a first radio station, radio resource controlfor a first cell served by the first radio station and a second cellserved by a second radio station, in order to perform carrieraggregation using the first and second cells. Further, the performingincludes receiving, from the first radio station, configurationinformation related to the radio resource control for the second cell.

In an eighth aspect, a program includes instructions for causing acomputer to perform a communication control method according to theabove-described fifth aspect.

In a ninth aspect, a program includes instructions for causing acomputer to perform a communication control method according to theabove-described sixth aspect.

In a tenth aspect, a program includes instructions for causing acomputer to perform a communication control method according to theabove-described seventh aspect.

Advantageous Effects of Invention

According to the above-described aspects, it is possible to provide aradio communication system, a radio station, a radio terminal, acommunication control method, and a program which are contribute toprevention or reduction of data transmission/reception failures whichwould otherwise occur while the configuration of radio parameters or thelike is being changed by a radio terminal in carrier aggregation of aplurality of cells served by different radio stations.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a configuration example of a radio communication systemaccording to a first embodiment;

FIG. 2 shows a configuration example of a first radio station accordingto the first embodiment;

FIG. 3 shows a configuration example of a second radio station accordingto the first embodiment;

FIG. 4 shows a configuration example of a radio terminal according tothe first embodiment;

FIG. 5 is a sequence diagram showing an example of a communicationcontrol method in a radio communication system according to the firstembodiment (Procedure Example 1);

FIG. 6 is a sequence diagram showing an example of a communicationcontrol method in a radio communication system according to the firstembodiment (Procedure Example 2);

FIG. 7 is a sequence diagram showing an example of a communicationcontrol method in a radio communication system according to the firstembodiment (Procedure Example 3);

FIG. 8 is a sequence diagram showing an example of a communicationcontrol method in a radio communication system according to a secondembodiment (Procedure Example 4);

FIG. 9 is a sequence diagram showing an example of a communicationcontrol method in a radio communication system according to the secondembodiment (Procedure Example 5);

FIG. 10 is a sequence diagram showing an example of a communicationcontrol method in a radio communication system according to the secondembodiment (Procedure Example 6); and

FIG. 11 is a sequence diagram showing a procedure for changing a radioresource configuration in carrier aggregation according to the LTE(Background Art).

DESCRIPTION OF EMBODIMENTS

Specific embodiments are explained hereinafter in detail with referenceto the drawings. The same symbols are assigned to the same orcorresponding elements throughout the drawings, and duplicatedexplanations are omitted as necessary.

First Embodiment

FIG. 1 shows a configuration example of a radio communication systemaccording to this embodiment. The radio communication system accordingto this embodiment includes a first radio station 1, a second radiostation 2, and a radio terminal 3. The radio stations 1 and 2 areconnected to a core network 4 and serve first and second cells 10 and20, respectively. Each of the radio stations 1 and 2 is, for example, aradio base station, a base station control station, or a simplifiedradio base station having only some of the functions (protocol layers)of an ordinary radio base station. The radio terminal 3 has a functionof, while using a cell of one radio base station, using a cell ofanother radio station. In other words, the radio terminal 3 supports acarrier aggregation (or cell aggregation) of a plurality of cells servedby different radio stations. Note that the different radio stations maybe different base stations independent of each other, or may be oneradio station and another radio base station dependent on the one radiostation. Further, the different radio stations may be radio stations ofdifferent types having different functions.

For example, the radio terminal 3 can establish a second radioconnection on the second cell 20 while maintaining a first radioconnection on the first cell 10. The expression “establishment of aradio connection” corresponds to, for example, a state where the radioterminal 3 can communicate with a radio station (e.g., the radio station1 or 2), or a state where the radio terminal 3 and a radio station(e.g., the radio station 1 or 2) possess common information necessaryfor communication therebetween. In this way, the radio terminal 3 cansimultaneously use a plurality of cells (e.g., the cells 10 and 20) fortransmitting or receiving signals (e.g., user data or controlinformation). The expression “simultaneous use of a plurality of cells”is not limited to actual simultaneous reception or transmission ofsignals in a plurality of cells. That is, it includes: a state where theradio terminal actually receives or transmits signals in either one ofthe cells although the radio terminal is able to receive or transmitsignals in both of the cells; a state where the radio terminal receivesor transmits signals of different types in the respective cells; and astate where the radio terminal uses each of the plurality of cells foreither signal reception or signal transmission.

In view of the carrier aggregation of a plurality of cells served bydifferent radio stations, the function of using a plurality of cellsserved by different radio stations can be called “inter-radio stationcarrier aggregation”. Further, in view of the above-describedsimultaneous use of a plurality of cells, the function of using aplurality of cells served by different radio stations can also be called“Dual Connection”, “Dual Connectivity”, “Multi Connection”, “MultiConnectivity”, or the like.

The radio terminal 3 may transmit to the radio station 1 or the radiostation 2 a terminal capability report indicating that the radioterminal 3 is capable of performing inter-radio station carrieraggregation (i.e., supports inter-radio station carrier aggregation).Alternatively, the radio terminal 3 may implicitly indicate that theradio terminal 3 supports inter-radio station carrier aggregation by thecategory of the radio terminal 3 or its device release number. Thecapability of performing inter-radio station carrier aggregation canalso be called “dual-connection capability” or “multi-connectioncapability”.

FIG. 1 shows a Heterogeneous Network (HetNet) environment. Specifically,the first cell 10 shown in FIG. 1 has coverage wider than that of thesecond cell 20. Further, FIG. 1 shows a hierarchical cell structure inwhich the second cell 20 is disposed inside the first cell 10. Note thatthe cell structure shown in FIG. 1 is merely an example. For example,the first and second cells 10 and 20 may have the same degree ofcoverage. In other words, the radio communication system according tothis embodiment may be applied to a Homogeneous Network environment.

Next, an operation of the radio communication system according to thisembodiment is explained in a more detailed manner. In a radiocommunication system according to this embodiment, the first radiostation 1 has control and management functions (e.g., an RRC layer) forthe first and second cells 10 and 20 for performing inter-radio stationcarrier aggregation of the first and second cells 10 and 20.Specifically, the first radio station 1 performs, with the radioterminal 3, radio resource control for the cells 10 and 20 in order toperform carrier aggregation of the cells 10 and 20. The first radiostation 1 may transmit a configuration related to the radio resourcecontrol to the radio terminal 3 in the first cell 10, or may transmitthe configuration to the radio terminal 3 in the second cell 20 throughthe second radio station 2. In the latter case, although the first radiostation 1 transmits to the second radio station 2 a message containingthe configuration related to the radio resource control for the secondcell 20, the second radio station 2 does not necessarily have torecognize the contents of that message. Alternatively, the second radiostation 2 may recognize the contents of the message. When the secondradio station 2 transmits the configuration related to the radioresource control in the second cell 20, the second radio station 2 maytransmit the configuration in a manner similar to that for transmittingother downlink data. The first radio station 1 is also configured totransmit, to the second base station 2, update information regarding anupdate to the configuration related to the radio resource control forthe second cell 20.

The above-described update information transmitted from the first radiostation 1 to the second radio station 2 triggers, for example, a stop ora suspension of at least one of downlink transmission and uplinkreception in the second cell 20 performed by the second radio station 2.The above-described update information may explicitly or implicitlyindicate, for example, at least one of the following items (a) to (d):

(a) A start report about a start of the update (or a change) to theconfiguration related to the radio resource control for the second cell20;(b) A start notification of a start of the update (or a change) to theconfiguration related to the radio resource control for the second cell20;(c) An advance notification of the update (or a change) to theconfiguration related to the radio resource control for the second cell20; and(d) A completion prediction of the completion of the update (or achange) to the configuration related to the radio resource control forthe second cell 20.

When the above-described update information indicates a start report ofthe update (i.e., the update has already been started), a startnotification of the update (i.e., the update is about to be started), oran advance notification of the update (i.e., the update is scheduled tobe started from now), the first radio station 1 may transmit informationindicating an end timing (or a prediction of an end timing) of theupdate to the configuration related to the radio resource control forthe second cell 20 together with the start report, the startnotification, or the advance notification. Alternatively, the firstradio station 1 may transmit to the second radio station 2 a completionnotification when the update to the configuration related to the radioresource control for the second cell 20 has been completed.

When the above-described update information is an advance notificationof the update, the first radio station 1 may transmit information aboutupdate (start) timing together with the update advance notification.

The information about the update (start) timing or the information aboutthe end timing of the update, which is indicated by the above-describedupdate information, may be indicated using, for example, a timer valueor by a frame number (e.g., System Frame Number (SFN)).

The above-described update information does not necessarily have to be asimple update notification or a simple update advance notification. Thatis, the above-described update information may be a configurationrelated to the radio resource control for the second cell 20 that is thesame as the configuration to be transmitted from the first radio station1 to the radio terminal 3, or control information related to thatconfiguration. Further, the configuration or the control information maybe transmitted from the first radio station 1 using an inter-radiostation control message. In this case, upon receiving the controlmessage, the second radio station 2 may determine that the second radiostation 2 has implicitly received the start report, start notification,or advance notification of the update (or the change) to theconfiguration related to the radio resource control for the second cell20. That is, the first radio station 1 may implicitly notify the secondradio station 2 of one of the above-listed items (a) to (d) bytransmitting to the second radio station 2 the configuration related tothe radio resource control for the second cell 20, which is to beupdated, or the control information related to that configuration.

The first radio station 1 may individually transmit the above-describedupdate information to the second radio station 2 for each radio terminal3, or collectively transmit it to the second radio station 2 for aplurality of or all of radio terminals 3 that perform communication inthe second cell 20.

The first radio station 1 may transmit to the second radio station 2 theabove-described update information (i.e., the update informationregarding the update to the configuration related to the radio resourcecontrol for the second cell 20) together with update informationregarding an update to a configuration related to radio resource controlfor a cell(s) other than the second cell 20 (e.g., the first cell 10).Alternatively, the first radio station 1 may transmit update informationregarding an update to a configuration related to radio resource controlfor the first cell 10 as the above-described update information (i.e.,the update information regarding the update to the configuration relatedto the radio resource control for the second cell 20).

Upon receiving the above-described update information (i.e., the updateinformation regarding the update to the configuration related to theradio resource control for the second cell 20), the second radio station2 may operate, for example, as follows. The second radio station 2controls signal transmission and/or reception to and/or from the radioterminal 3 in the second cell 20. In an example, the second radiostation 2 may stop or suspend at least one of signal transmission to theradio terminal 3 and signal reception from the radio terminal 3 in thesecond cell 20 while the update to the configuration related to theradio resource control for the second cell 20 is being performed or isexpected to be performed by the radio terminal 3.

Next, control and management for the first and second cells 10 and 20performed by the first radio station 1 is explained. The first radiostation 1 transmits, for example, a configuration related to the radioresource control for the cells 10 and 20 to the radio terminal 3 in thefirst cell 10. The radio terminal 3 transmits and/or receives signals inaccordance with the received configuration related to the radio resourcecontrol. In an example, upon receiving the configuration related to theradio resource control, the radio terminal 3 may refrain fromtransmitting and receiving signals (e.g., data) in the second cell 20during the period in which the radio terminal 3 is performing orupdating the configuration related to the radio resource control for thesecond cell 20. In this period, the radio terminal 3 may transmit andreceive signals in the first cell 10 as usual, or may also refrain fromtransmitting and/or receiving signals (e.g., data) in the first cell 10.

The configuration related to the radio resource control for the cells 10and 20 may be, but is not limited to, a configuration of radioparameters or the like. For example, the configuration related to theradio resource control may include at least one of a radio parameterconfiguration, a terminal measurement configuration, a configurationrelated to a certain function, and a secondary configuration.

The first radio station 1 may individually transmit the configurationinformation related to the radio resource control for the second cell 20(in other words, an instruction about the configuration or theconfiguration update) to each radio terminal 3 in the first cell 10, orcollectively transmit it to a plurality of or all of radio terminals 3that perform communication in the first cell 10 by using a commonmessage.

As described above, in this embodiment, the first radio station 1performs and updates, with the radio terminal 3 in the first cell 10,the configuration related to the radio resource control for the secondcell in order to perform the inter-radio station carrier aggregation ofthe cells 10 and 20. Further, the first radio station 1 transmits, tothe second radio station 2, update information regarding the update tothe configuration related to the radio resource control for the secondcell 20. As a result, the second radio station 2 can recognize that theupdate to the configuration related to the radio resource control forthe second cell 20 is performed by the radio terminal 3. Therefore, forexample, the second radio station 2 can stop or suspend at least one ofsignal transmission to the radio terminal 3 and signal reception fromthe radio terminal 3 in the second cell 20 while the update to theconfiguration related to the radio resource control for the second cell20 is being performed or is expected to be performed in the radioterminal 3. As a result, this embodiment can contribute to prevention orreduction of data transmission/reception failures which would otherwiseoccur while the configuration of radio parameters or the like is beingchanged by the radio terminal 3.

Next, configuration examples of the radio stations 1 and 2 and the radioterminal 3 according to this embodiment are explained. FIG. 2 is a blockdiagram showing a configuration example of the first radio station 1. Aradio communication unit 11 receives an uplink signal transmitted fromthe radio terminal 3 thorough an antenna. A reception data processingunit 13 restores the received uplink signal. The obtained reception datais forwarded to another network node such as a data transfer device or amobility management device in the core network 4, or to other radiostations through a communication unit 14. For example, uplink user datareceived from the radio terminal 3 is forwarded to a data transferdevice in a higher-layer network. Further, non-access stratum (NAS)control data among control data received from the radio terminal 3 isforwarded to a mobility management device in a higher-layer network.Further, the reception data processing unit 13 receives, from acommunication control unit 15, control data to be transmitted to theradio station 2, and transmits this control data to the radio station 2through the communication unit 14.

A transmission data processing unit 12 acquires user data destined forthe radio terminal 3 from the communication unit 14 and generates atransport channel by performing error correction encoding, ratematching, interleaving, and the like. Further, the transmission dataprocessing unit 12 generates a transmission symbol sequence by addingcontrol information to the data sequence of the transport channel. Theradio communication unit 11 generates a downlink signal by performingcarrier modulation based on the transmission symbol sequence, frequencyconversion, signal amplification, and the like, and transmits thegenerated downlink signal to the radio terminal 3. Further, thetransmission data processing unit 12 receives control data to betransmitted to the radio terminal 3 from the communication control unit15 and transmits this control data to the radio terminal 3 through theradio communication unit 11.

The communication control unit 15 controls inter-radio station carrieraggregation of the first and second cells 10 and 20. Specifically, thecommunication control unit 15 performs, with the radio terminal 3 in thefirst cell 10, radio resource control for the cells 10 and 20 in orderto perform carrier aggregation of the cells 10 and 20. Further, thecommunication control unit 15 transmits to the second radio station 2the update information regarding the update to the configuration relatedto the radio resource control for the second cell 20.

FIG. 3 is a block diagram showing a configuration example of the secondradio station 2. The functions and the operations of a radiocommunication unit 21, a transmission data processing unit 22, areception data processing unit 23, and a communication unit 24 shown inFIG. 3 are similar to those of their corresponding elements shown inFIG. 2, i.e., those of the radio communication unit 11, the transmissiondata processing unit 12, the reception data processing unit 13, and thecommunication unit 14.

A communication control unit 25, in the radio station 2, controlsinter-radio station carrier aggregation of the first and second cells 10and 20. Further, the communication control unit 25 receives from thefirst radio station 1 the update information regarding the update to theconfiguration related to the radio resource control for the second cell20. In an example, the communication control unit 25 may stop or suspendat least one of downlink transmission and uplink reception in the secondcell 20 during a period specified based on the received updateinformation (i.e., a period in which the update to the configurationrelated to the radio resource control for the second cell 20 is beingperformed or is expected to be performed in the radio terminal 3).

FIG. 4 is a block diagram showing a configuration example of the radioterminal 3. A radio communication unit 31 supports carrier aggregationof a plurality of cells served by different radio stations, and is ableto simultaneously use the plurality of cells (e.g., the cells 10 and 20)for transmitting or receiving signals. Specifically, the radiocommunication unit 31 receives a downlink signal from one or both of theradio stations 1 and 2 through an antenna. A reception data processingunit 32 restores reception data from the received downlink signal andsends the restored reception data to a data control unit 33. The datacontrol unit 33 uses the reception data according to its purpose.Further, a transmission data processing unit 34 and a radiocommunication unit 31 generate an uplink signal by using transmissiondata supplied from the data control unit 33 and transmit the generateduplink signal to one or both of the radio stations 1 and 2.

A communication control unit 35, in the radio terminal 3, controlsinter-radio station carrier aggregation of the first and second cells 10and 20. Further, the communication control unit 35 receives, from thefirst radio station 1 in the first cell 10, the configuration related tothe radio resource control for the cells 10 and 20, and performs orupdates the configuration for the radio resource control for the cells10 and 20. In an example, the communication control unit 35 may stop orsuspend at least one of signal transmission to the second radio station2 and signal reception from the second radio station 2 in the secondcell 20 while the radio terminal 3 is performing or updating theconfiguration related to the radio resource control for the second cell20.

Next, Procedure Examples 1 to 3 of a communication control method in aradio communication system according to this embodiment are explainedhereinafter.

Procedure Example 1

In Procedure Example 1, the first radio station 1 transmits, to theradio station 2, the update information regarding the update to theconfiguration related to the radio resource control for the radioterminal 3 in the second cell 20. FIG. 5 shows an example of a sequencediagram showing a communication control method according to theProcedure Example 1. In steps S101 and S102, the radio terminal 3performs carrier aggregation of the first and second cells 10 and 20.That is, in the steps S101 and S102, the first radio station 1 transmitsand/or receives data or control information to and/or from the radioterminal 3 in the first cell 10, and meanwhile the second radio station2 transmits and/or receives data to and/or from the radio terminal 3 inthe second cell 20.

In a step S103, the first radio station 1 determines that theconfiguration related to the radio resource control for the second cell20 needs to be changed, and hence transmits, to the second radio station2, the update information regarding the update to the configurationrelated to the radio resource control for the second cell 20. In a stepS104, the second radio station 2 transmits and/or receives data toand/or from the radio terminal 3 in the second cell 20 while takingaccount of the update information received in the step S103. In oneexample, the second radio station 2 does not transmit or receive data toor from the radio terminal 3 while the configuration related to theradio resource control for the second cell 20 is being changed in theradio terminal 3. Accordingly, data transmission in the second cell 20is appropriately performed and packet losses and the like can beprevented.

Note that though it is not clearly shown in FIG. 5, in the ProcedureExample 1, the second radio station 2 may also change the configurationof the radio resource control for the second cell 20. For example, theupdate information regarding the update to the configuration related tothe radio resource control, which is transmitted from the first radiostation 1, includes configuration information related to the radioresource control that should be changed by the second radio station 2.The second radio station 2 may change the configuration related to theradio resource control for the second cell 20 upon receiving theconfiguration information. Alternatively, the second radio station 2 maychange the configuration related to the radio resource control for thesecond cell 20 at the same timing as that at which this configuration ischanged in the radio terminal 3. The configuration information relatedto the radio resource control that should be changed by the second radiostation 2 may be different for each radio terminal 3 that performscommunication in the second cell 20, or may be common to a plurality ofor all of radio terminals 3 that perform communication in the secondcell 20. The use of the common configuration information can reduce thenumber of signals transmitted between the radio stations 1 and 2.

Procedure Example 2

In Procedure Example 2, the first radio station 1 transmits, to thesecond radio station 2, a start notification of the update (i.e., anotification that the update is about to be started) as the updateinformation regarding the update to the configuration related to theradio resource control for the radio terminal 3 in the second cell 20.Further, the first radio station 1 notifies the second radio station 2that the radio terminal 3 has completed the update to the configurationrelated to the radio resource control.

FIG. 6 shows an example of a sequence diagram showing a communicationcontrol method according to the Procedure Example 2. In a step S201, thefirst radio station 1 determines that the configuration related to theradio resource control for the second cell 20 needs to be changed, andhence transmits, to the second radio station 2, a start notification ofthe update to the configuration as the update information regarding theupdate to the configuration related to the radio resource control. In astep S203, the first radio station 1 transmits, to the radio terminal 3,configuration information related to the radio resource control for thesecond cell 20.

The radio terminal 3 updates the configuration related to the radioresource control for the second cell 20 according to the receivedconfiguration information and reports the completion of the update tothe first radio station 1 (step S203). The radio terminal 3 may refrainfrom transmitting and receiving signals (e.g., data) in the second cell20 while the radio terminal 3 is updating the configuration related tothe radio resource control for the second cell 20.

In a step S204, the first radio station 1 notifies the second radiostation 2 that the UE 3 has completed the update to the configurationrelated to the radio resource control for the second cell 20. In a stepS205, the second radio station 2 resumes or starts data transmissionand/or reception to and/or from the radio terminal 3 in the second cell20. As described above, the second radio station 2 does not transmit orreceive data to or from the radio terminal 3 while the configurationrelated to the radio resource control for the second cell 20 is beingchanged in the radio terminal 3. Accordingly, data transmission in thesecond cell 20 is appropriately performed and packet losses and the likecan be prevented.

In the Procedure Example 2, the update information regarding the updateto the configuration related to the radio resource control, which istransmitted in the step S201, may include information about update(start) timing of that configuration or may include informationindicating that the update to that configuration has been started.

In the Procedure Example 2, similarly to the supplementary explanationin the Procedure Example 1, the second radio station 2 may also changethe configuration of the radio resource control for the second cell 20.For example, the update information regarding the update to theconfiguration related to the radio resource control, which istransmitted from the first radio station 1, includes configurationinformation related to the radio resource control that should be changedby the second radio station 2.

Procedure Example 3

In Procedure Example 3, the first radio station 1 transmits to thesecond radio station 2, as the update information regarding the updateto the configuration related to the radio resource control for the radioterminal 3 in the second cell 20, a start notification of the update(i.e., a notification that the update is about to be started) andinformation indicating a completion prediction of the update to theconfiguration performed by the radio terminal 3 (e.g., a timer value).

FIG. 7 shows an example of a sequence diagram showing a communicationcontrol method according to the Procedure Example 3. In a step S201, thefirst radio station 1 determines that the configuration related to theradio resource control for the second cell 20 needs to be changed, andhence transmits to the second radio station 2, as the update informationregarding the update to the configuration related to the radio resourcecontrol, information indicating a start notification of the update tothe configuration and information indicating the completion predictionof the update to the configuration performed by the radio terminal 3.The information indicating the prediction of the completion is, forexample, a timer value (a timer configuration value). The second radiostation 2 activates a timer according to the timer value, i.e., thesecond radio station 2 starts measurement. The timer is used todetermine the completion (or the prediction of the completion) of theupdate to the configuration related to the radio resource control.

In a step S302, the first radio station 1 transmits, to the radioterminal 3, configuration information related to the radio resourcecontrol for the second cell 20. The radio terminal 3 updates theconfiguration related to the radio resource control for the second cell20 according to the received configuration information and reports thecompletion of the update to the first radio station 1 (step S303). Theradio terminal 3 may refrain from transmitting and receiving signals(e.g., data) in the second cell 20 while the radio terminal 3 isupdating the configuration related to the radio resource control for thesecond cell 20.

The second radio station 2 resumes or starts data transmission and/orreception to and/or from the radio terminal 3 in the second cell 20after the timer (i.e., the timer value) has expired (step S304). Notethat, the information indicating the prediction of the completion of theupdate to the configuration related to the radio resource control may bea frame number (e.g., an SFN) or the like instead of the time value. Inthe example, the second radio station 2 does not transmit and receivedata to and from the radio terminal 3 while the configuration related tothe radio resource control for the second cell 20 is being changed inthe radio terminal 3. Accordingly, data transmission in the second cell20 is appropriately performed and packet losses and the like can beprevented.

In the Procedure Example 3, the update information regarding the updateto the configuration related to the radio resource control, which istransmitted in the step S301, may include information about update(start) timing of that configuration or may include informationindicating that the update to that configuration has been started.

In the Procedure Example 3, similarly to the supplementary explanationin the Procedure Example 1, the second radio station 2 may also changethe configuration of the radio resource control for the second cell 20.For example, the update information regarding the update to theconfiguration related to the radio resource control, which istransmitted from the first radio station 1, includes configurationinformation related to the radio resource control that should be changedby the second radio station 2.

Second Embodiment

In this embodiment, an example where the above-described firstembodiment is applied to a 3GPP LTE system is explained. A configurationexample of a radio communication system according to this embodiment maybe similar to that shown in FIG. 1. Note that the radio stations 1 and 2correspond to eNBs, the radio terminal 3 corresponds to an UE, and thecore network 4 corresponds to an EPC (Evolved Packet Core). Transmissionand reception of information between radio stations (i.e., between eNBs)may use an X2 interface, which is a direct interface, may use an S1interface through the EPC, or may use a newly-defined interface (e.g.,an X3 interface). The following explanation is given on the assumptionthat: the radio stations 1 and 2 are eNBs 1 and 2; the radio terminal 3is an UE 3; and the core network 4 is an EPC 4.

The radio terminal (UE) 3 can establish a second radio connection in thesecond cell 20 (Cell 20) while maintaining a first radio connection inthe first cell 10 (Cell 10). The expression “establishment of a radioconnection” corresponds to, for example, a state where the UE 3 cancommunicate with an eNB (e.g., the eNB 1 or 2) (e.g., a state where RRCConnection Setup has already been completed), or a state where the UE 3and an eNB (e.g., the eNB 1 or 2) possess common information (e.g., UEcontext) necessary for communication therebetween. More specifically,the UE 3 supports carrier aggregation of a plurality of cells served bydifferent radio stations (eNBs) (called “Inter-eNB CA” or “Inter-SiteCA”). Note that the term “Inter-eNB CA” in this specification is notlimited to actual simultaneous reception or transmission of signals indifferent eNB cells. For example the “Inter-eNB CA” includes: a statewhere the radio terminal (UE) actually receives or transmits signals(e.g., user data or control information) in either one of the eNB cellsalthough the UE 3 is able to receive or transmit signals in both of thedifferent eNB cells; a state where the radio terminal receives ortransmits signals of different types in the respective cells ofdifferent eNBs; and a state where the radio terminal uses each of thecells of different eNBs for either signal reception or signaltransmission.

As an example to which this embodiment is applied, it is conceivablethat the UE 3 performs inter-radio base station carrier aggregation(Inter-eNB CA) in which the UE 3 uses the Cell 20 of the eNB 2 as asecondary cell (SCell) while the UE 3 is already using the Cell 10 ofthe eNB 1 as a primary cell (PCell). The primary cell (PCell) is a cellthat has already been used since before the CA is started. In contrastto this, the second cell (SCell) is a cell that is used (activated) inaddition to the PCell or in dependence thereon on the precondition thatthe UE 3 is already connected to the primary cell. Non-Access Stratum(NAS) mobility information, security information (or security input),and the like are transmitted and received through the PCell when a radioconnection is established (i.e., at the time of RRC ConnectionEstablishment) or reestablished (i.e., at the time of RRC ConnectionRe-establishment). A DL Component Carrier used for the PCell is a DLPCC, and an UL Component Carrier used for the PCell is an UL PCC.Similarly, a DL Component Carrier used for the SCell is a DL SCC, and anUL Component Carrier used for the SCell is an UL SCC.

The radio terminal (UE) 3 establishes a radio connection (RRCConnection) with the first radio base station (eNB) 1 in the first cell10 (Cell 10, e.g., PCell), and establishes a radio connection with thesecond radio base station (eNB) 2 in the second cell 20 (Cell 20, e.g.,SCell). The eNB 1 has control and management functions (e.g., an RRClayer) in the Cell 10 and the Cell 20. Specifically, the eNB 1 preforms,with the UE 3, radio resource control for the Cell 10 and the Cell 20 inorder to perform carrier aggregation of the Cell 10 and the Cell 20. TheeNB 1 may transmit a configuration related to the radio resource controlto the UE 3 in the Cell 10, or may transmit the configuration to the UE3 through the Cell 20 via the eNB 2. In the latter case, although theeNB 1 transmits a message including the configuration, which is relatedto the radio resource control for the Cell 20, to the eNB 2 through anX2 interface or an S1 interface (or a new interface), the eNB 2 does notnecessarily have to recognize the contents of that message.Alternatively, the eNB 2 may recognize the contents of the message. Whenthe eNB 2 transmits the configuration related to the radio resourcecontrol in the Cell 20, the eNB 2 may transmit the configuration on aData Radio Bearer (DRB) in a manner similar to that for transmittingother data. The eNB 1 is also configured to transmit, to the eNB 2,update information (Radio Resource Configuration update information)regarding an update to the configuration related to the radio resourcecontrol for the Cell 20.

The above-described update information may explicitly or implicitlyindicate at least one of the following items (a) to (d):

(a) A start report about a start of the update (or a change) to theconfiguration related to the radio resource control for the Cell 20;(b) A start notification of a start of the update (or a change) to theconfiguration related to the radio resource control for the Cell 20;(c) An advance notification of the update (or a change) to theconfiguration related to the radio resource control for the Cell 20; and(d) A completion prediction of the completion of the update (or achange) to the configuration related to the radio resource control forthe Cell 20.

When the above-described update information indicates a start report ofthe update, a start notification of the update, or an advancenotification of the update, the eNB 1 may transmit information about anend timing (also called “Completion time”) (or a prediction of an endtiming) together with the start report, the start notification, or theadvance notification. The end timing indicates “a prediction of thecompletion of the update of the configuration related to the radioresource control for the Cell 20 (e.g., the SCell)”. Alternatively, theeNB 1 may transmit a completion notification of the update to theconfiguration related to the radio resource control for the Cell 20(e.g., the SCell) (Radio Resource Configuration update completeindication) upon completing the update to that configuration.

When the above-described update information is an update advancenotification, the eNB 1 may transmit information about an update (start)timing (also called “Activation time”) together with the update advancenotification.

The information about the update (start) timing or the information aboutthe end timing indicated by the above-described update information maybe, for example, a timer value or may be indicated by a frame number(e.g., an SFN).

The above-described update information does not necessarily have to be asimple update notification or a simple update advance notification. Thatis, the above-described update information may be information about aconfiguration related to the radio resource control for the Cell 20(e.g., the SCell) that is the same as the configuration to betransmitted from the eNB 1 to the UE 3, or control information relatedto that configuration. Further, the configuration information or thecontrol information may be transmitted from the eNB 1 using an inter-eNBcontrol message. In this case, upon receiving the control message, theeNB 2 may determine that the eNB 2 has implicitly received the startreport, start notification, or advance notification of the update (orthe change) to the configuration related to the radio resource controlfor the Cell 20 (e.g., the SCell).

The eNB 1 may individually transmit the above-described updateinformation to the eNB 2 for each UE 3, or collectively transmit it tothe eNB 2 for a plurality of or all of UEs 3 that perform communicationin the Cell 20 (e.g., the SCell).

The eNB 1 may transmit to the eNB 2 the above-described updateinformation (i.e., the update information regarding the update to theconfiguration related to the radio resource control for the Cell 20(e.g., the SCell)) together with update information regarding an updateto a configuration related to radio resource control for a cell(s) otherthan the Cell 20 (e.g., the Cell 10). Alternatively, the eNB 1 maytransmit update information regarding an update to a configurationrelated to radio resource control for the Cell 10 (e.g., the PCell) asthe above-described update information (i.e., the update informationregarding the update to the configuration related to the radio resourcecontrol for the Cell 20 (e.g., the SCell)).

Upon receiving the above-described update information (i.e., the updateinformation regarding the update to the configuration related to theradio resource control for the Cell 20), the eNB 2 may operate, forexample, as follows. The eNB 2 controls transmission and/or reception ofsignals (i.e., SRB or DRB) to and/or from the UE 3 in the Cell 20. In anexample, the eNB 2 may stop or suspend at least one of signaltransmission to the UE 3 and signal reception from the UE 3 in the Cell20 while the update to the configuration related to the radio resourcecontrol for the Cell 20 is being performed or is expected to beperformed in the UE 3.

Next, control and management for the Cell 10 (e.g., PCell) and the Cell20 (e.g., SCell) performed by the eNB 1 is explained. The eNB 1transmits, for example, a configuration related to the radio resourcecontrol for the Cells 10 and the Cell 20 to the UE 3 in the Cell 10. TheUE 3 transmits and/or receives signals in accordance with the receivedconfiguration related to the radio resource control. In an example, uponreceiving the configuration related to the radio resource control, theUE 3 may refrain from transmitting and receiving signals (e.g., data) inthe Cell 20 during the period in which the UE 3 is performing orupdating the configuration related to the radio resource control for theCell 20. In this period, the UE 3 may transmit/receive signals in theCell 10 as usual, or may also refrain from transmitting and/or receivingsignals (e.g., data) in the Cell 10.

The configuration related to the radio resource control for the Cell 10and the Cell 20 is, for example, a configuration of radio parameters orthe like transmitted by RRC signaling (e.g., RRC ConnectionReconfiguration) and includes at least one of the following items (a) to(d):

(a) A radio resource configuration (RadioResourceConfig);(b) A terminal measurement configuration (MeasConfig);(c) Other configurations related to a predetermined function(OtherConfig); and(d) A secondary cell configuration (e.g., SCellToAddModList or SCellToReleaseList).

Note that examples of the OtherConfig include: control informationrelated to a report from the UE 3 on detection of a Closed SubscriberGroup (CSG) Cell to which the UE 3 itself can be connected(ReportProximityConfig); control information related to interferenceamong radio systems included in the UE 3 (i.e., included in the radioterminal) (IDC-Config); control information related to an acquisition oflocation information by the UE 3 (ObtainLocationConfig); and controlinformation related to power consumption and transmission/receptioncharacteristics (e.g., throughput) of the UE 3(PowerPrefIndicationConfig).

Next, Procedure Examples 4 to 6 of a communication control method in aradio communication system according to this embodiment are explained.Note that it is assumed that the UE 3 performs inter-radio base stationcarrier aggregation (Inter-eNB CA) in which the UE 3 uses the Cell 20 ofthe eNB 2 as the SCell while the UE3 is already using the Cell 10 of theeNB 1 as the PCell.

Procedure Example 4

Procedure Example 4 corresponds to the Procedure Example 2 explained inthe first embodiment. That is, the eNB 1 transmits an update startnotification (configuration update indication) to the eNB 2 as theupdate information regarding the update to the configuration related tothe radio resource control for the UE 3 in the SCell (Radio ResourceConfiguration update information). Further, the eNB 1 notifies the eNB 2that the radio terminal 3 has completed the update to the configuration.

FIG. 8 shows an example of a sequence diagram showing the ProcedureExample 4. Note that in FIG. 8, the Cell 10 (i.e., the PCell) and theCell 20 (i.e., the SCell) are expressed as “CELL1” and “CELL2”,respectively. In steps S401 and S402, the UE 3 performs carrieraggregation of the CELL1 and the CELL2. That is, in the steps S401 andS402, the eNB 1 transmits and/or receives data or control information toand/or from the UE 3 in the CELL1 and meanwhile the eNB 2 transmitsand/or receives data to and/or from the UE 3 in the CELL2.

In a step S403, the eNB 1 determines that the configuration related tothe radio resource control for the CELL2 (SCell) needs to be changed,and hence transmits, to the eNB 2, a start notification of the update tothe configuration as the update information regarding the update to theconfiguration related to the radio resource control. In a step S404, theeNB 1 transmits, to the UE 3, configuration information related to theradio resource control for the CELL2 (RRC Connection Reconfigurationincluding updated CELL2 configuration).

In a step S405, the UE 3 updates the configuration related to the radioresource control for the CELL2 according to the received configurationinformation and reports the completion of the update to the eNB 1 (RRCConnection Reconfiguration Complete). The UE 3 may refrain fromtransmitting and receiving signals (e.g., data) in the CELL2 while theUE 3 is updating the configuration related to the radio resource controlfor the CELL2.

In a step S406, the eNB 1 notifies the eNB 2 that the UE 3 has completedthe update to the configuration related to the radio resource controlfor the CELL2 (Radio Resource Configuration update complete indication).In a step S407, the eNB 2 resumes or starts data transmission and/orreception to and/or from the UE 3 in the CELL2. The eNB 2 does nottransmit or receive data to or from the UE 3 while the configurationrelated to the radio resource control for the CELL2 (SCell) is beingchanged in the UE 3. Accordingly, data transmission in the SCell isappropriately performed and packet losses and the like can be prevented.Note that the eNB 1 may also refrain from transmitting and receivingdata to and from the UE 3 in the PCell while the configuration relatedto the radio resource control for the SCell is being changed in the UE3.

In the Procedure Example 4, the update information regarding the updateto the configuration related to the radio resource control, which istransmitted in the step S403, may include information about update(start) timing of that configuration or may include informationindicating that the update to that configuration has been started.

Note that though it is not clearly shown in FIG. 8, in the ProcedureExample 4, the eNB 2 may also change the configuration of the radioresource control for the CELL2. For example, the update informationregarding the update to the configuration related to the radio resourcecontrol, which is transmitted from the eNB 1, includes configurationinformation related to the radio resource control that should be changedby the eNB 2. The eNB 2 may change the configuration related to theradio resource control for the CELL2 upon receiving this configurationinformation. Alternatively, the eNB 2 may change the configurationrelated to the radio resource control for the CELL2 at the same timingat which this configuration is changed in the UE 3. The configurationinformation related to the radio resource control that should be changedby the eNB 2 may be different for each UE 3 that performs communicationin the CELL2, or may be common to a plurality of or all of UEs 3 thatperform communication in the CELL2. The use of the common configurationinformation can reduce the number of signals transmitted between theeNBs 1 and 2.

Procedure Example 5

Procedure Example 5 corresponds to the Procedure Example 3 explained inthe first embodiment. That is, the eNB 1 transmits to the eNB 2, as theupdate information regarding the update to the configuration related tothe radio resource control for the UE 3 in the SCell (Radio ResourceConfiguration update information), an update start notification(configuration update indication) and a timber value (timerconfiguration value) indicating a prediction of the completion of theupdate to that configuration performed by the UE 3 (expected completiontime).

FIG. 9 shows an example of a sequence diagram showing the ProcedureExample 5. Note that in FIG. 9, the first cell 10 (i.e., the PCell) andthe second cell 20 (i.e., the SCell) are expressed as “CELL1” and“CELL2”, respectively. In steps S501 and S502, the UE 3 performs carrieraggregation of the CELL1 and the CELL2. That is, in the steps S501 andS502, the eNB 1 transmits and/or receives data or control information toand/or from the UE 3 in the CELL1 and meanwhile the eNB 2 transmitsand/or receives data to and/or from the UE 3 in the CELL2.

In a step S503, the eNB 1 determines that the configuration related tothe radio resource control for the CELL2 (SCell) needs to be changed,and hence transmits to the eNB 2, as the update information regardingthe update to the configuration related to the radio resource control, astart notification of the update to the configuration and a timer valueindicating a prediction of the completion of the update to theconfiguration performed by the UE 3. The eNB 2 activates a timeraccording to the received timer value, i.e., the eNB 2 startsmeasurement. The timer is used to determine the completion (or theprediction of the completion) of the update to the configuration relatedto the radio resource control.

In a step S504, the eNB 1 transmits, to the UE 3, configurationinformation related to the radio resource control for the CELL2 (RRCConnection Reconfiguration including updated CELL2 configuration). In astep S505, the UE 3 updates the configuration related to the radioresource control for the CELL2 and reports the completion of that updateto the eNB 1 (RRC Connection Reconfiguration Complete). The UE 3 mayrefrain from transmitting and receiving signals (e.g., data) in theCELL2 while the UE 3 is updating the configuration related to the radioresource control for the CELL2.

The eNB 2 resumes or starts data transmission and/or reception to and/orfrom the UE 3 in the CELL2 after the timer has expired (step S506). Notethat, the information indicating the prediction of the completion of theupdate to the configuration related to the radio resource control may bea frame number (e.g., an SFN) or the like instead of the time value. Inthe example, the eNB 2 does not transmit and receive data to and fromthe UE 3 while the configuration related to the radio resource controlfor the CELL2 (SCell) is being changed in the UE 3. Accordingly, datatransmission in the SCell is appropriately performed and packet lossesand the like can be prevented.

In the Procedure Example 5, the update information regarding the updateto the configuration related to the radio resource control, which istransmitted in the step S503, may include information about update(start) timing of that configuration or may include informationindicating that the update to that configuration has been started.

In the Procedure Example 5, similarly to the supplementary explanationin the Procedure Example 4, the eNB 2 may also change the configurationof the radio resource control for the SCell. For example, the updateinformation regarding the update to the configuration related to theradio resource control, which is transmitted from the eNB 1, includesconfiguration information related to the radio resource control thatshould be changed by the eNB 2.

Procedure Example 6

In Procedure Example 6, the eNB 1 transmit, to the eNB 2, an advancenotification of a start of the update (expected configuration updateinformation), as the update information regarding the update to theconfiguration related to the radio resource control for the UE 3 in theSCell (Radio Resource Configuration update information). Further, inthis example, an update to system information (System Information Block(SIB)) is assumed as the configuration related to the radio resourcecontrol in the SCell. That is, a notification of an update to the systeminformation of the second cell 20, which serves as the SCell, istransmitted in the first cell 10, which serves as the PCell.Alternatively, as described previously, the eNB 1 may notify the UE 3 ofthe update to the system information of the second cell 20 through thesecond cell 20 via the eNB 2.

FIG. 10 shows an example of a sequence diagram showing the ProcedureExample 6. Note that in FIG. 10, the first cell 10 (i.e., the PCell) andthe second cell 20 (i.e., the SCell) are expressed as “CELL1” and“CELL2”, respectively. Further, FIG. 10 also shows n number of UEs 3(UE1, . . . , UEn in FIG. 10) that communicate with the eNB 2 in theCELL2.

In steps S601 and S602, the eNB 2 transmits and/or receives data toand/or from the n number of UEs 3 in the CELL2. In a step S603, the eNB1 determines that the system information, which is the configurationrelated to the radio resource control for the CELL2 (SCell), needs to bechanged, and hence transmits to the eNB 2 an advance notification of theupdate to the system information of the CELL2 and the contents of thesystem information to be updated (e.g., a radio parameter).

In steps S604 and S605, the eNB 1 transmits configuration informationrelated to the radio resource control for the CELL2 (i.e., informationsuch as a radio parameter or the like included in the system informationin the Procedure Example 6) to the n number of UEs 3 (UE1, . . . , UEnin FIG. 10) that are using the CELL 2 in addition to the CELL1 (RRCConnection Reconfiguration including updated CELL2 configuration). Insteps S606 and S607, the n number of UEs 3 update the configurationrelated to the radio resource control for the CELL2 according to thereceived configuration information and report the completion of thatupdate to the eNB 1 (RRC Connection Reconfiguration Complete). Each UE 3may refrain from transmitting and receiving signals (e.g., data) in theCELL2 while the UE 3 is updating the configuration related to the radioresource control for the CELL2.

In a step S608, at a timing for updating the system information of theCELL2 (Modification period boundary) comes, the eNB 2 updates the systeminformation based on the updated contents (such as a radio parameter) ofthe system information received from the eNB 1 (Update CELL2configuration).

In steps S609 and S610, the eNB 2 resumes or starts data transmissionand/or reception to and/or from the n number of UEs 3 in the CELL2. Asdescribed above, the eNB 2 does not transmit and receive data to andfrom the UEs 3 while the configurations related to the radio resourcecontrol for the CELL2 (SCell) are being changed in the respective UEs 3.Accordingly, data transmission in the SCell is appropriately performedand packet losses and the like can be prevented.

Modification of Procedure Example 6

The eNB 1 may transmit the configuration information, which is relatedto the radio resource control for the n number of UEs 3 in the CELL2, inthe CELL1 at the same timing as the update timing of the systeminformation in the eNB 2 (CELL2), or may transmit the configurationinformation in the CELL1 immediately after that update timing.

The eNB 1 may transmit the configuration information, which is relatedto the radio resource control for the n number of UE 3 in the CELL2, toa predetermined UE group including one or more UEs (i.e., on agroup-by-group basis) by using a common message. Alternatively, the eNB1 may transmit the configuration information, related to the radioresource control for the CELL2, to all the UEs 3 located in the CELL1 byusing a common message. Further, alternatively, the eNB 1 may transmitthe configuration information, related to the radio resource control forthe CELL2, to the UEs 3 that use both the CELL1 and the CELL2 by using acommon message. In this way, the amount of the use of radio resources inthe CELL1 necessary for transmitting the configuration informationrelated to the radio resource control for the CELL2 can be reduced.

In the case where the eNB 1 transmits a common message to a plurality ofUEs 3, each of the UEs 3 that have received the configurationinformation related to the radio resource control by that commonmessage, i.e., each of the UEs 3 that have been instructed to update theconfiguration related to the radio resource control, may report thecompletion of the update to the configuration to the eNB 1 by using apredetermined common response message.

The eNB 1 may notify the n number of UEs 3 that the configurationrelated to the radio resource control for the CELL2 (the systeminformation in this example) is to be updated (e.g., by using paging),instead of transmitting the configuration information related to theradio resource control for the CELL2 to the n number of UEs 3 in theCELL 1. In this case, in response to receiving the notification (e.g.,paging) from the eNB 1, the n number of UEs 3 may voluntarily receivethe system information in the CELL2 at or immediately after the updatetiming of the system information. Each UE 3 may refrain fromtransmitting and receiving data in the CELL2 until it properly receivethe updated system information.

OTHER EMBODIMENTS

In the first and second embodiments, the radio station 1 may transmit,to the radio station 2 through a core network (e.g., an EPC), the updateinformation regarding the update to the configuration related to theradio resource control.

In the first and second embodiments, examples in which the radioterminals (UE) are individually controlled are mainly explained.However, for example, the configuration related to the radio resourcecontrol may be used in common for a plurality of radio terminals (UEs),or may be used in common for all the radio terminals (UEs) located inthe same cell. Accordingly, with regard to the notification method ofthe configuration information related to the radio resource control, theconfiguration information may be transmitted to a plurality of radioterminals (UEs) by using a common message, or may be transmitted to allthe radio terminals (UEs) located in the same cell by using a commonmessage (e.g., by using system information).

The first and second embodiments can be applied to a case where thefirst radio station 1 (eNB 1) is a macro radio base station (Macro eNB(MeNB)) that serves (manages) a macro cell having a relatively largecoverage and the second radio station 2 (eNB 2) is a low-power radiobase station (Low Power Node (LPN)) that serves (manages) a cell havinga small coverage. Examples of a LPN include a pico-radio base station(Pico eNB: PeNB) having functions similar to those of the MeNB and a newtype of network node (New Node) having fewer functions than those of theMeNB. Further, the second cell 20 may be a new type of cell (New CellType) which is different from conventional cells and uses a new type ofcarrier (New Carrier Type) different from conventional carriers.

Each of the communication control methods performed by the radio station1 (communication control unit 15), the radio station 2 (communicationcontrol unit 25), and the radio terminal 3 (communication control unit35) described in the first and second embodiments may be implemented byusing a semiconductor processing device such as an Application SpecificIntegrated Circuit (ASIC). Alternatively, these methods may beimplemented by causing a computer system including at least oneprocessor (e.g., Microprocessor, Micro Processing Unit (MPU), or DigitalSignal Processor (DSP)) to execute a program. Specifically, one or moreprograms including instructions for causing a computer system to performalgorithms shown in the flowcharts and the sequence diagrams may becreated, and these programs may be supplied to a computer.

These programs can be stored in various types of non-transitory computerreadable media and thereby supplied to computers. The non-transitorycomputer readable media includes various types of tangible storagemedia. Examples of the non-transitory computer readable media include amagnetic recording medium (such as a flexible disk, a magnetic tape, anda hard disk drive), a magneto-optic recording medium (such as amagneto-optic disk), a CD-ROM (Read Only Memory), a CD-R, and a CD-R/W,and a semiconductor memory (such as a mask ROM, a PROM (ProgrammableROM), an EPROM (Erasable PROM), a flash ROM, and a RAM (Random AccessMemory)). Further, these programs can be supplied to computers by usingvarious types of transitory computer readable media. Examples of thetransitory computer readable media include an electrical signal, anoptical signal, and an electromagnetic wave. The transitory computerreadable media can be used to supply programs to computer through a wirecommunication path such as an electrical wire and an optical fiber, orwireless communication path.

In the first and second embodiments, an LTE system has been mainlyexplained. However, these embodiments may be applied to radiocommunication systems other than the LTE system, such as a 3GPPUniversal Mobile Telecommunications System (UMTS), a 3GPP2 CDMA2000system (1×RTT, High Rate Packet Data (HRPD)), a Global System for MobileCommunications (GSM) system, and a WiMAX system.

Further, the above-described embodiments are merely examples for theapplication of the technical ideas obtained by the present inventors.Needless to say, these technical ideas are not limited to theabove-described embodiments and various modifications can be madethereto.

This application is based upon and claims the benefit of priority fromJapanese patent applications No. 2013-033704, filed on Feb. 22, 2013,the disclosure of which is incorporated herein in its entirety byreference.

REFERENCE SIGNS LIST

-   1 FIRST RADIO STATION-   2 SECOND RADIO STATION-   3 RADIO TERMINAL-   10 FIRST CELL-   20 SECOND CELL-   15 COMMUNICATION CONTROL UNIT-   25 COMMUNICATION CONTROL UNIT-   35 COMMUNICATION CONTROL UNIT

1. A method for a Master base station which operates a first cell,comprising: configuring Dual Connectivity which is for a radio terminalusing the first cell and a second cell which is operated by a Secondarybase station, transmitting, to the Secondary base station, informationrelated to configuration changes of the second cell, and transmitting,to the radio terminal via the Secondary base station, a Radio ResourceControl (RRC) message including radio resource configuration of thesecond cell.